Plasma β ‐amyloid and duration of Alzheimer's disease in adults with Down syndrome

Objectives To investigate the relation of plasma levels of A β peptides (A β 1‐40 and A β 1‐42) and apolipoprotein E (APOE) genotype to dementia status, and the duration of Alzheimer's disease (AD) in adults with Down syndrome (DS). Methods Adults with DS were recruited from community settings and followed up for a mean period of 6.7 years. Plasma levels A β 1‐40 and A β 1‐42 and APOE genotype were determined at the last visit. Results There were 83 nondemented participants and 44 participants with prevalent AD. Overall, plasma levels of A β 1‐42, A β 1‐40 and the ratio A β 1‐42/A β 1‐40 did not differ significantly between the adults with DS. Among demented participants, the mean level of A β 1‐40 was significantly lower (157.0 vs. 195.3) and the ratio of A β 1‐42/A β 1‐40 was significantly higher (0.28 vs . 0.16) in those with more than 4 years duration of dementia than in those with 4 or fewer years' duration of dementia. This pattern was generally similar in those with and without an APOE ε 4 allele. Conclusions There is an association between plasma A β peptide levels and the duration of AD in older persons with DS. The predictive and diagnostic roles of A β 1‐42 and A β 1‐40 measurements for AD, however, remain controversial. Change in A β peptide levels with onset of AD and with the duration of dementia may account for a lack of difference between prevalent cases and nondemented individuals and for variation in the predictive power of A β peptide levels. Copyright © 2009 John Wiley & Sons, Ltd.